There are many different piston designs used, for example, in air compressors, combustion engines, or in hydraulic actuators, among others. For example, in a hydraulic actuator, hydraulic fluid pushes against one side of a piston located within a bore to cause translation of a rod attached thereto. Typically the rod is connected to a member which is displaced in accordance with the translation of the piston within the bore.
In FIG. 1, a conventional arrangement is shown where a piston (A) resides in a bore (B) having means for applying fluid pressure to one side of the piston which results in translation of a rod (C) attached thereto. This rod may be used for example to position the rotor blades of a helicopter aircraft for blade fold storage. Of course, such actuators have many different applications.
One problem with these and other piston arrangements is that there is a rigid connection of the piston to the rod. Such a rigid connection locks the piston to the rod such that when bending loads are applied to the rod, they are transmitted to the piston which may cock within the bore. For example, if the actuator were used on an aircraft, flexing of the associated aircraft structures may cause such cocking of the piston and thereby result in excessive wear of the bore which in turn leads to leakage of the hydraulic fluid. Also, misalignment or eccentricities do occur due to tolerance stack-ups in manufacturing and assembly. Even in assemblies where the piston is pinned to a rod, such as a connecting rod in a combustion engine, such pinned type connections allow misalignment to be absorbed only in one direction, the direction about which the connecting rod is rotatable. In all other directions, it is a rigid connection and thus side loads could cause cocking of the piston and result in excessive bore wear.